The present invention relates to an ultraviolet and infrared radiation absorbing glass having a high visible light transmittance and a green tint. More particularly, the invention relates to an ultraviolet and infrared radiation absorbing green glass which, when heat-tempered before use, is inhibited from changing in color through the heat-tempering and which is hence especially suitable for use as an automotive window glass.
In order to meet the demand for protection of interior trim of automobiles against deterioration, which has been increasing with the recent trend to luxury of the interior trim, and to reduce the load of air conditioning, various glasses having ultraviolet and infrared radiation absorbing power have recently been proposed as automotive window glasses.
Among the automotive window glasses, the front or side window glasses should have a visible light transmittance of not less than a certain value so as to secure driver""s view. Glasses which have been designed for use in such a position and to which ultraviolet radiation absorbing properties and heat radiation absorbing properties have been imparted, have a greenish tint because an end of the ultraviolet absorption range and an end of the infrared absorption range reside in the visible region.
Window glasses which have an ultraviolet transmittance of about 38% or less and a total solar energy transmittance of about 46% or less and which further have a visible light transmittance of at least 70% so as to secure a view from the inside of the automobile have conventionally been known (see, for example, JP-A-3-187946). (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d.)
It is known that one method effective in reducing the total solar energy transmittance of a glass is to increase the absolute amount of ferrous oxide among the iron oxides contained in the glass. Most of the infrared radiation absorbing glasses which have been proposed so far are produced with this technique.
On the other hand, various techniques for reducing ultraviolet transmittance have been proposed. For example, the infrared and ultraviolet radiation absorbing glass disclosed in JP-A-4-193738 contains cerium oxide and titanium oxide so as to have a reduced ultraviolet transmittance. This glass comprises, in % by weight, base glass components comprising 68 to 72% SiO2, 1.6 to 3.0% Al2O3, 8.5 to 11.0% CaO, 2.0 to 4.2% MgO, 12.0 to 16.0% Na2O, and 0.5 to 3.0% K2O and, coloring components comprising 0.65 to 0.75% Fe2O3, 0.20 to 0.35% CeO2, and 0.2 to 0.4% TiO2.
The ultraviolet radiation absorbing glass disclosed in JP-A-6-56466 which has a green tint, comprises a soda-lime-silica glass as base glass components and, coloring components comprising 0.53 to 0.70% total iron oxide in terms of Fe2O3, 0.5 to 0.8% CeO2, and 0.2 to 0.4% TiO2, wherein 30 to 40% of the total iron oxide in terms of Fe2O3 is accounted for by FeO in terms of Fe2O3.
The ultraviolet and infrared radiation absorbing glass disclosed in JP-B-6-88812 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) which has a green tint comprises, in % by weight, base glass components comprising 65 to 75% SiO2, 0 to 3% Al2O3, 1 to 5% MgO, 5 to 15% CaO, 10 to 15% Na2O, and 0 to 4% K2O and, coloring components comprising 0.65 to 1.25% total iron oxide in terms of Fe2O3 and either 0.2 to 1.4% CeO2 or a combination of 0.1 to 1.36% CeO2 and 0.02 to 0.85% TiO2.
Furthermore, glasses which have a preferred tint by adding nickel oxide have been proposed. For example, the glass disclosed in JP-W-8-506314 (the term xe2x80x9cJP-Wxe2x80x9d as used herein means an xe2x80x9cunexamined published PCT applicationxe2x80x9d) comprises a soda-lime-silica glass having a ferrous content calculated with the following equation:
FeO (wt %)xe2x89xa70.007+[(optical density)xe2x88x920.036]/2.3 and contains 0.25 to 1.75% by weight Fe2O3. It further contains one or more members selected from the group consisting of Se, Co3O4, Nd2O3, NiO, MnO, V2O5, CeO2, TiO2, CuO, and SnO and thereby has an neutral tint. This glass has a visible light transmittance of 32% or more, an ultraviolet transmittance of 25% or less, and a solar heat radiation transmittance lower by at least 7% than the visible light transmittance, when it has a thickness of 4 mm. It preferably has a dominant wavelength shorter than 570 nm.
The glasses disclosed in the patent documents cited above have ultraviolet radiation absorbing power by Fe2O3, CeO2, and TiO2 and by interactions among them. However, glasses containing these ingredients assume a yellow tint through heat-tempering. Although the reasons for this color change are unclear, it may be due to the fact that an increase in absorption is observed, which is presumably attributable mainly to an interaction between Fe2O3 and CeO2. Because of this, a glass plate produced and a glass plate obtained by processing (heat-tempering) the glass plate so as to be actually usable as an automotive window glass differ in tint. In this respect, those conventional glasses have had a drawback in quality control. In particular, an increase in saturation caused by heat-tempering is undesirable because the color becomes more vivid.
On the other hand, in the glasses containing NiO, the color change through heat-tempering can be inhibited due to the absorption by tetra-coordinated NiO after heat-tempering in combination with the coloration in yellow mentioned above. However, the conventional glasses containing NiO have too low a visible light transmittance or too high an ultraviolet or infrared transmittance and are hence unsatisfactory for use as automotive window glasses.
The invention has been made in the light of the above-described circumstances of the conventional techniques. An object of the invention is to provide an ultraviolet and infrared radiation absorbing green glass which has a high visible light transmittance, a low ultraviolet transmittance, and a low infrared transmittance, changes little in color through heat-tempering, and retains a stable green tint. Another object of the invention is to provide an ultraviolet and infrared radiation absorbing green glass which, in addition to these properties, has a lower total solar energy transmittance than conventional ones due to the infrared absorption by NiO and which therefore is especially suitable for use as an automotive window glass.
(1) The invention provides an ultraviolet and infrared radiation absorbing green glass comprising: in % by weight,
as coloring components,
0.5 to 1.1%, excluding 0.5%, total iron oxide in
terms of
Fe2O3 (Txe2x80x94Fe2O3);
0 to 2.0% CeO2;
0 to 1.0% TiO2;
0.0005 to 0.01% NiO; and
0.0001 to 0.001% CoO;
wherein, when the glass has a thickness of 4 mm, the glass has a visible light transmittance (YA) of 70% or more, a total solar energy transmittance (TG) of 60% or less, and an ultraviolet transmittance defined by ISO 9050 (Tuv) of 25% or less
(2) In the glass of the invention, the preferred content of CeO2 is from 0.1 to 2.0% by weight.
(3) The glass of the invention preferably comprises: in % by weight,
as base glass components,
65 to 80% SiO2;
0 to 5% Al2O3;
0 to 10% MgO;
5 to 15% CaO:
10 to 20% Na2O;
0 to 5% K2O; and
0 to 5% B2O3;
wherein the sum of MgO and CaO is 5 to 15% and the sum of Na2O and K2O is 10 to 20%.
(4) In the glass of the invention, the content of Txe2x80x94Fe2O3 is preferably from 0.6 to 1.1%, excluding 0.6%.
(5) FeO in terms of Fe2O3 preferably accounts for 20 to 60% of the Txe2x80x94Fe2O3.
(6) The glass of the invention preferably contains 0.0001 to 0.1% in total of at least one selected from the group consisting of Se, Cr2O3, Mn2O3, CuO, Nd2O3, Er2O3, MoO3, V2O5, and La2O3.
(7) The glass of the invention preferably, when the glass has a thickness of 4 mm, has a visible light transmittance (YA) of 70% or more, a total solar energy transmittance (TG) of 53% or less, and an ultraviolet transmittance defined by ISO 9050 (Tuv) of 20% or less.
(8) In the glass of the invention, the difference in a saturation between the glass before a heat treatment and that after the treatment is preferably within 0.5. The saturation is determined from chromaticities a* and b* in the CIE 1976 L*a*b* color system using the following equation (1) (hereinafter referred to as xe2x80x9csaturationxe2x80x9d):
Saturation=(a*2+b*2)1/2xe2x80x83xe2x80x83(1)
(9) The heat treatment is preferably a heat-tempered treatment by air blast cooling.
(10) The glass is especially preferably a sheet glass formed by the float process and has undergone heat-tempering.
Modes for carrying out the invention will be described below in detail.
First, the reasons for limitations of the composition of the ultraviolet and infrared radiation absorbing green glass according to the invention are explained below. Hereinafter, all percents used for component amounts are by weight.
Iron oxide in a glass is present in the forms of Fe2O3, and FeO. Fe2O3is a component which serves to enhance ultraviolet radiation absorbing power, while FeO is a component which serves to enhance heat radiation absorbing power.
If the amount of the total iron oxide in terms of Fe2O3 (Txe2x80x94Fe2O3) is less than 0.5%, the effect of absorbing ultraviolet and infrared radiation is so low that the desired optical properties cannot be obtained. On the other hand, contents of Txe2x80x94Fe2O3 exceeding 1.1% are undesirable in that the glass has a reduced visible light transmittance. Such too high Txe2x80x94Fe2O3 contents are undesirable also in that, when this glass and a glass having a different composition are successively produced with the same glass melting furnace, the compositional change requires much time. Consequently, the content of Txe2x80x94Fe2O3 is from 0.5 to 1.1%, excluding 0.5%, preferably from 0.6 to 1.1%, excluding 0.6%.
NiO is a component for regulating visible light transmittance and color tone. In the invention, NiO plays an especially important role in controlling the color tones before and after a heat treatment. If the content of NiO is less than 0.0005%, the sufficient effect cannot be obtained. On the other hand, contents thereof exceeding 0.01% are undesirable in that the visible light transmittance is decreased.
It is known that NiO changes in coordination number depending on the cooling rate of the glass, resulting in a different color tone. Specifically, the coordination number for the oxygen surrounding Ni2+ changes from 6 to 4 through heat-tempering, and this change brings about a change in absorption. Ni2+ of octahedral coordination has absorption at around 430 nm to color the glass yellow-brown, while Ni2+ of tetrahedral coordination has absorption in the range of from 500 to 640 nm. In the invention, this property of NiO is utilized to control the color tones before and after a heat treatment.
CoO is a component for obtaining a green tint in cooperation with NiO and Fe2O3, and further serves to control visible light transmittance. If the content of CoO is less than 0.0001%, a desirable green tint cannot be obtained. If the content of CoO exceeds 0.001%, the results are too intense a blue tint and a reduced visible light transmittance.
CeO2, although not an essential component, is a component which enhances ultraviolet radiation absorbing power. CeO2 in a glass is present in the form of Ce3+ or Ce4+. In particular, Ce3+ shows reduced absorption in the visible region and is effective in ultraviolet absorption. Ce3+ functions also to enhance ultraviolet radiation absorbing power by an interaction with Fe3+. The content of CeO2 is preferably not less than 0.1%, whereby, a sufficient ultraviolet radiation absorbing power can be obtained. Use of CeO2 in an amount more than 2% is undesirable in that the results are an increased cost and a reduced visible light transmittance.
TiO2, although not an essential component, serves to enhance ultraviolet radiation absorbing power by an interaction with FeO. It may be added in an appropriate amount. If the content of TiO2is too high, the glass tends to be yellowish. Consequently, the upper limit of TiO2 content should be 1.0%, and is preferably 0.8%, more preferably 0.1%.
From the standpoint of obtaining the green tint and properties which the invention is intended to attain, it is preferred that at least one member selected from the group consisting of Se, Mn2O3, CuO, Cr2O3, Nd2O3, Er2O3, MoO3, V2O5 and La2O3 can be added to a glass having a composition within the range according to the invention in an amount of from 0.0001 to 0.1%. Se, Mn2O3, CuO, Cr2O3, Nd2O3 and Er2O3 can function as auxiliary coloring agents and MoO3, V2O5 and La2O3 can function as auxiliary ultraviolet absorbers.
SiO2 is a main component forming a skeleton of glass. If the content of SiO2 is less than 65%, the glass has poor durability. If the content thereof exceeds 80%, the glass is difficult to melt.
Al2O3 is a component which improves glass durability. It the content of Al2O3 exceeds 5%, the glass is difficult to melt. The preferred range of Al2O3 content is from 0.1 to 2%.
MgO and CaO both are used for improving glass durability and for regulating the liquidus temperature and viscosity of the glass during forming. If the content of MgO exceeds 10%, the liquidus temperature rises. If the content of CaO is less than 5% or higher than 15%, the liquidus temperature rises. If the total content of MgO and CaO is less than 5%, the glass has poor durability. If the total content thereof exceeds 15%, the liquidus temperature rises.
Na2O and K2O accelerate glass melting. If the content of Na2O is less than 10% or if the total content of Na2O and K2O is less than 10%, the effect of melting acceleration is poor. If the content of Na2O exceeds 20% or if the total content of Na2O and K2O exceeds 20%, glass durability is decreased. Since too large K2O amounts result in an increased cost, it is desirable to use K2O in an amount of 5% or less.
B2O3 is a component used for improving glass durability or as a melting aid. It functions also to enhance ultraviolet absorption. If the content of B2O3 exceeds 5%, troubles arise in glass forming due to vaporization of B2O3, etc. Consequently, the upper limit of B2O3 content should be 5%.
If the ratio of the amount of FeO to that of Txe2x80x94Fe2O3 is too small, sufficient heat radiation absorbing power cannot be obtained because of the too small FeO amount. On the other hand, if the FeO/Txe2x80x94Fe2O ratio is too large, the range of absorption by FeO extends even into a longer-wavelength range in the visible region, so that the glass has a reduced visible light transmittance and a blue tint. Furthermore, too large FeO/Txe2x80x94Fe2O3 ratios are undesirable in that since the melt of such a glass is on the reduction side, there are cases where not only nickel sulfide stones generate in the glass but also silica-rich streaks or a silica scum generates. In the invention, the FeO/Txe2x80x94Fe2O3 ratio is preferably regulated to 20 to 60%, whereby a green glass having high ultraviolet absorbing power and high heat radiation absorbing power is obtained. The FeO amount used for expressing the FeO/Txe2x80x94Fe2O3 ratio is a value calculated in terms of Fe2O3.
It is preferred to add at least one of Sb2O3, SnO2, and the like as a reducing agent or refining agent in a total amount of up to 1%. It is also preferred to add up to 1% ZnO in order to prevent the generation of nickel sulfide stones more surely.
The glass of the invention has a composition within such a range that the glass can be inhibited from suffering a color change through a heat treatment. Consequently, the difference between the saturation, indicating color tone, of the glass before a heat treatment and that after the treatment is preferably within 0.5. Namely, the glass which has undergone the heat treatment preferably has a reduced saturation.
The main use of the glass according to the invention is as an automotive window glass. For the purpose of safety, the glass is usually heat-tempered by air blast cooling.
The invention will be described in more detail by reference to the following Examples and Comparative Examples.